Wireless communication systems based on a multicarrier scheme, such as orthogonal frequency-division multiplexing (OFDM) based communication systems, are gaining worldwide popularity due to their broad applications. The multicarrier scheme allows a multicarrier communication system to operate on multiple carriers including continuous and discontinuous carriers. Each of the multiple carriers corresponds to a relatively narrow frequency band, and may have a different bandwidth.
Traditionally, a separate fast Fourier transform (FFT) and radio frequency (RF) module may be used for each band, and a medium access control (MAC) module may then be used in the multicarrier communication system to support multicarrier functionalities. Based on different capabilities of different user terminals, a network side, such as a base station (BS), a Node B defined in a Universal Mobile Telecommunications System (UMTS) standard, or an access point (AP), may serve different user terminals with different bandwidths. For example, based on the multicarrier scheme, the base station may flexibly use available bandwidth resources to achieve high throughput and capacity.
For controlling and utilizing the multiple carriers, each of the multiple carriers may be classified as a primary carrier, also known as a fully configured carrier, or a secondary carrier, also known as a partially configured carrier. For example, a primary carrier is typically used to transmit both control information and data, and a secondary carrier is typically used to only transmit data. Depending on characteristics of transmission of control information and data, a downlink control method may use different downlink control structures for a primary carrier and a secondary carrier.
FIG. 1 illustrates a conventional downlink control method 100 for use in a multicarrier communication system based on IEEE standard 802.16m. For convenience of illustration, a frame structure 102 is shown for a primary carrier CH0, a first secondary carrier CH1, and a second secondary carrier CH2 of the multiple carriers of the multicarrier system. For example, the frame structure 102 may include a plurality of super-frames, such as first and second super-frames 104 and 106. Each of the plurality of super-frames may further include a plurality of frames. Based on the IEEE standard 802.16m, each of the plurality of super-frames may include four frames 112, 114, 116, and 118. Traditionally, three control channels, including a synchronization control channel (SCH) 122, a broadcast control channel (BCH) 124, and a unicast service control channel (USCCH) 126, may be used for downlink control.
For example, the SCH 122 may provide a reference signal for time, frequency, frame synchronization, and base station identification. The SCH 122 may be only allocated to the primary carrier CH0. In addition, the SCH 122 may be transmitted on the primary carrier CH0 every one or more frames, such as every four frames as shown in FIG. 1, and a location of the SCH 122 may be fixed in each of the plurality of super-frames. The secondary carriers CH1 and CH2 may share the SCH 122 with the primary channel CH0.
Also for example, the BCH 124 may provide system configuration information and broadcast information, such as neighbor base station information, paging information, etc. The BCH 124 may be only allocated to the primary carrier CH0. In addition, the BCH 124 may be transmitted on the primary carrier CH0 every one or more frames, such as every four frames as shown in FIG. 1, and a location of the BCH 124 may be fixed in each of the plurality of super-frames. The secondary carriers CH1 and CH2 may share the BCH 124 with the primary channel CH0.
Further for example, the USCCH 126 may provide resource allocation for unicast services. The USCCH 126 may be allocated to the primary carrier CH0 and the secondary carriers CH1 and CH2. In addition, the USCCH 126 and the SCH 122 are transmitted at different times, and the USCCH 126 and the BCH 124 are also transmitted at different times.